Molt-accelerating compounds such as Mach 2 insecticide are considered biorational products because they mimic natural substances. Molting is the process of losing skin.

Registered Biorationals

New laws may limit the use of many traditional turf chemicals. Many natural substances and organisms fall under the category of biorational pesticides. Biorational pesticides are third-generation pesticides that are environmentally sound and closely resemble or are identical to chemicals produced in nature.

By now, anyone who uses pesticides should be familiar with the Food Quality Protection Act (FQPA), a U.S. law enacted in 1996. The law's primary goal is to reduce the risk of human exposure to pesticides to acceptable levels while preserving critical pesticide uses (2). All currently registered pesticides must eventually (based on a time-line determined by the EPA) undergo a risk assessment.

Ultimately, decisions made under the FQPA will have a major impact on the number of products available for use on turf, and many of the most commonly used products could be lost (1).

In response, many chemical manufactures have decided to develop and market alternative or new pest-control products that are "softer," or pose less potential risk to humans and the environment. These alternative products include biorational pesticides or biopesticides, as well as some novel chemicals with substantially lower use rates.

What is a biorational pesticide?
The terms biorational pesticide and biopesticide are rapidly gaining popularity in the current climate of environmental awareness and public concern (3). These terms are derived from two words, biological and rational, referring to pesticides of natural origin that have limited or no adverse effects on the environment or beneficial organisms (4).

There is, however, actually no legally clear, absolute definition of a biorational pesticide. The EPA considers biorational pesticides to have different modes of action than conventional or traditional pesticides, with greater selectivity and considerably lower risks to humans, wildlife and the environment.

A biorational pesticide is derived from a variety of biological sources, including bacteria, viruses, fungi and protozoa, as well as chemical analogues of naturally occurring biochemicals such as pheromones and insect growth regulators (IGRs). They are considered third-generation pesticides that are environmentally sound and closely resemble or are identical to chemicals produced by insects and plants (4).

Biorational products are quite different from conventional, broad-spectrum products. They do not control pests in the same way as most broad-spectrum products. They are typically target-specific and have little to no impact on non-target organisms.

Most biorational insecticides are much more effective against some insect pests than others. As a result, proper identification of a target insect pest is essential. Turfgrass managers must also understand both the limitations and strengths of biorational products.

For example, many biorational insecticides have relatively short residual activity compared with conventional products. Thus, biorational products must be applied when the pest is in its most vulnerable life stage. Otherwise, applications may be ineffective, and applications of a conventional product may be necessary.

Nematodes, visble here as tiny white worms feeding inside a white grup's carcass, offer an alternative to chemical insecticides.

Classification
Biorational insecticides are classified into two distinct groups: biochemical and microbial. Biochemical products include hormones, enzymes, pheromones and natural insect and plant growth regulators. Microbial products originate from biological organisms such as bacteria, fungi, nematodes, protozoa and viruses.

Biochemical products

Insect pheromones are chemical substances that are given off by insects and cause a specific reaction upon reception by another insect of the same species. Releaser pheromones are fast-acting and are used by insects for sexual attraction, aggregation, dispersion, oviposition (egg laying) and alarm or warning. Primer pheromones are slow-acting and cause gradual changes in growth and development. Of these types of pheromones, sexual attraction pheromones offer the greatest potential for insect control.

There are four primary uses for sex pheromones in present insect-control programs: male trapping, movement monitoring, detection and population monitoring, and confusion.

In turf, sex pheromones are used in traps to detect and monitor Japanese beetle populations. However, traps are not effective in controlling this pest. Each use of sex pheromones offers its own limitations and benefits.

Insect growth regulators (IGRs) are chemical compounds that alter the growth and development of insects. IGRs disrupt an insect's growth and development in two basic ways: as juvenile hormones and as chitin synthesis inhibitors.

Juvenile hormones prevent insects from maturing; they force an insect to remain in its juvenile life stage (immature, caterpillar or grub stage). Juvenile hormones are not effective in controlling turfgrass insect pests such as armyworm (Pseudaletia unipuncta) larvae, cutworm larvae, sod webworm (Crambus teterellus) larvae or white grubs because the juvenile is the damaging life stage of these pests.

Much of the exterior (skin) and even some of the internal parts of an insect are constructed of chitin (a polymer). Chitin synthesis products inhibit the production of chitin, resulting in the inability of an insect to produce new exoskeletons (skin). And, without an exoskeleton, insects cannot survive. A chitin synthesis inhibitor would be an appropriate control product for the turfgrass insect pests mentioned above.

Microbial products

Bacillus thuringiensis (Bt) is a spore-forming bacterium that produces toxins that, after ingestion, cause a rapid gut paralysis and death of certain insects, especially caterpillars. Bt is a naturally occurring soil bacterium, but chemical manufacturers have developed a process to formulate it and make it commercially available to turfgrass managers.

Bt complements many environmentally sensitive pest management programs because of its low toxicity. As a result, Bt is the most widely used microbial insecticide in the turfgrass and ornamental markets (3). However, Bt is not a "silver-bullet;" like all control products, it has limitations. Bt has a relatively short-residual activity; is readily degraded by direct sunlight; has slow action, limited-contact activity; and is unable to kill larger larvae. Success with Bt depends on close monitoring and application when insects are small or in their most vulnerable life stage.

Bacillus popilliae is a spore-forming bacterium, the causal agent of milky disease in white grubs of the Japanese beetle and other scarab beetles. Several strains of milky disease bacteria infect various species of white grubs; each strain tends to be specific for that type of grub (3). The bacteria are harmless to earthworms, wildlife and humans, as well as beneficial insects. Like Bt, milky disease spores have been formulated and marketed. It was available under the trade names Doom and Japidemic, and now it is again being marketed under the trade name Milky Spore.

Milky disease also has limitations. It is very slow-acting -- even under ideal conditions it takes several years for the pathogen to provide adequate control of grub populations. In addition, milky spore disease is relatively expensive, and much of the research data on this product has shown an extremely variable pattern of performance (3).

Beauveria bassiana is a naturally occurring fungus that infects several insects. Spores of the fungus adhere to the insect skin and upon germination, penetrate the body wall, eventually killing the insect. Beauvaria bassiana has limitations as well: Similar to other fungi, it typically requires hot, moist conditions to be effective. More research is needed on fungus-based insecticides to better understand how they may be used in a turfgrass pest management program.

Entomopathogenic nematodes are microscopic roundworms that attack and kill insect caterpillars and grubs, and they continue their life cycle by reproducing within the dead host. These types of nematodes are beneficial organisms that naturally occur in most soils and are not considered a threat to plants and wildlife other than insects. They pose no threat of contamination to streams, lakes or groundwater. Entomopathogenic nematodes are mass-produced and marketed by only a limited number of manufacturers. Unfortunately, factors such as poor or short shelf-life, sensitivity to heat and sunlight, and speed of kill have limited the use of nematodes. These factors, compounded by the decision of some companies to discontinue marketing nematodes, have reduced nematode availability.

Spinosad is in a relatively new class of insecticides called naturalytes that contain two fermentation-derived substances produced by the bacterium Saccharopolyspora spinosa. This bacterium is a naturally occurring microorganism that acts as both a contact and a stomach poison, but is more effective if eaten by the insect pest. Spinosad is similar to conventional synthetic pyrethroids in that it is effective at very low use rates and has a fairly short residual activity. Spinosad, however, affects the insect nervous system by causing tremors, rapid paralysis and death. Because of the aforementioned characteristics and its low toxicity to humans and wildlife, spinosad may become an important resource for turfgrass managers.

The future
Biorational pesticides will become important resources for turfgrass managers and their pest-management programs. Demand will likely grow for these new tools as the EPA implements restrictions on pesticide uses, registration and labeling, and as chemical manufacturers voluntarily remove or decline to produce chemicals for turf to preserve more lucrative markets.

Literature cited
1. Brandenburg, R.L. 1999. Food Quality Protection Act may limit pesticide choices. Golf Course Management 67(2):58-61.

2. Guillebeau, P. 1998. Food Protection may limit pesticide use. Golf Course Management 66(1):62-66.

3. Potter, D.A. 1998. Destructive turfgrass insects: biology, diagnosis, and control. Ann Arbor Press, Chelsea, Mich.

4. Ware, G.W. 1989. The pesticide book, 3rd edition. Thomas Publications, Fresno, Calif.

R. Chris Williamson, Ph.D., is a turfgrass and ornamental entomologist at the University of Wisconsin-Madison.